Expression of receptors for human angiogenin in vascular smooth muscle cells

Human angiogenin is a plasma protein with angiogenic and ribonucleolytic ac tivities. Angiogenin inhibited both DNA replication and proliferation of ao rtic smooth muscle cells. Binding of I-125-angiogenin to bovine aortic smoo th muscle cells at 4 degrees C was specific, saturable, reversible and invo lved two families of interactions. High-affinity binding sites with an appa rent dissociation constant of 0.2 nM bound 1 x 10(4) molecules per cell gro wn at a density of 3 x 10(4).cm(-2). Low-affinity binding sites with an app arent dissociation constant of 0.1 mu M bound 4 x 10(6) molexcules.cell(-1) . High-affinity binding sites decreased as cell density increased and were not detected at confluence. I-125-angiogenin bound specifically to cells ro utinely grown in serum-free conditions, indicating that the angiogenin-bind ing components were cell-derived. Affinity labelling of sparse bovine smoot h muscle cells yielded seven major specific complexes of 45, 52, 70, 87, 98 , 210 and 250-260 kDa. The same pattern was obtained with human cells. Pote ntial modulators of angiogenesis such as protamine, heparin and the placent al ribonuclease inhibitor competed for angiogenin binding to the cells. Tog ether these data suggest that cultured bovine and human aortic smooth muscl e cells express specific receptors for human angiogenin.